Apparatus for making light weight aggregate



June 6, 1961 H. MCNALLY APPARATUS FOR MAKING LIGHT WEIGHT AGGREGATEFiled Nov. 5. 1958 NNMR T INVENTOR. Howoro L. M9 N0//y United StatesPatent C) 2,986,77 3 APPARATUS FOR MAKING LIGHT WEIGHT AGGREGATE HowardL. McNally, Mount Pleasant, Mich., assignor to The Dow Chemical(Iompany, Midland, Mich., a corporation of Delaware Filed Nov. 5, 1958,Ser. No. 772,097 7 Claims. (Cl. 18-2.6)

This invention relates to an apparatus for converting molten slag tolight weight aggregate which is suitable for use in the buildingmaterials industry.

The problem of disposing of molten slicate slag such as boiler furnaceslag or of converting the slag to a useful marketable product has longbeen a serious one. Various types of conversion apparatus havepreviously been used to convert other types of slags such as blastfurnace slag, to a light weight aggregate. The conversion is usuallyaccomplished in conventional converters by subjecting molten slag totreatment by steam (or to water which is vaporized by the slag to formsteam). When used in the conversion of blast furnace slag, the lightcomprising an inverted cup-shaped conversion chamber 12 having sidewalls 60 which diverge outwardly inthe.

downward direction and having a rotatable agitator, indicated generallyby the numeral 14, attached to a shaft 16- extending axially through theclosed upper end 18 of the chamber 12. The side walls diverge outwardlynot less than 5 degrees and preferably not more than 10 degrees Meanssuch as a,

is provided for feeding particulated carbonaceous ma terial, such aspulverized coal, for example, into the chamber 12. A water cooled duct,indicated generally by the numeral 24, disposed below the conversionchamber 12 and a conveyor 13 is disposed beneath the outlet end 26 ofthe duct 24 to receive the globules of expanded,

slag which fall through the conversion chamber 12and through the duct24. The conversion apparatus 10 is supported above the conveyor by meansof a suitable supporting frame not shown.- The side walls 25 of theweight aggregate formed thereby is often suitable for use as anaggregate material in the making of building blocks in which highstructural strength is not required.

Apparatus used in processing blast furnace slag has not, however, provedvery satisfactory when used in processing other silicate slags such asboiler furnace slag, which is an iron aluminum silicate type of slag.

For example, attempted conversion of boiler slag in apparatus of thewater or steam contact type used in converting blast furnace slag hasresulted in an expanded product which is more dense than is desired foruse as a light weight aggregate material, has non-uniform or substandardstrength characteristics, or the apparatus simply does not operate wellas -a continuously operating means for converting molten boiler slag.

Accordingly, a principal object of this invention is to provide animproved apparatus for converting molten silicate slag to a light weightaggregate material suitable for use in building materials.

Another object of this invention is to provide an improved apparatus forconverting molten iron aluminum silicate type slag to light weightaggregate of generally uniform cellular structure and strengthcharacteristics.

In accordance with this invention pulverized gas liberating material,usually a carbonaceous material, is mixed with molten slag as the slagis being violently agitated. The molten slag, impregnated with particlesof gas liberating material, expands as the gas is liberated, expandingthe slag into a light weight mass having a cellular structure asthe-slag is cooled in a controlled manner.

As a specific example of the operation of the invention, molten slag andpulverized carbonaceous material, such as bituminous coals, are fed intoa walled chamber and impinge on a rotating beater contained therein. Therotating beater intimately mixes the slag and carbonaceous material,causing globules of the mixture to be thrown against the cooled wall ofthe chamber. The cooling and expanding globules move downwardly andbreak away from the wall and fall into a conveyor.

The invention, as well as additional objects and advantages thereof,will best be understood when the following detailed description is readin connection with the accompanying drawings, in which:

" FIG. 1 is a side elevational view, partly in section, of slagconversion apparatus made in accordance with this invention, and

FIG. 2 is a sectional view taken along the line 22 of FIG. 1.

Referring to the drawings, there is shown the slag conversion apparatus,indicated generally by the numeral 10,

duct 24 should be either parallel with the vertical axis of. the chamber12 or converge downwardly not more than 10 degrees and preferably notmore than 5 degrees.

The agitator 14 comprises a plate 30, conveniently made. circular inshape, for example, which has a flat upper sur-,

face 32 facing the input openings 34, 36 for slag and particulatedcarbonaceous materials, respectively. Four beater bars 38a, 38b, 38c,38d are disposed on the upper surface of the plate 30. While the beaters38a-38d may be disposed generally radially with respect to the shaft 16,the heaters 38a-38d may advantageously be displaced a short distancelaterally from a true radial array to pro: duce a fanning or airpropelling action when the beaters are rotated.

The shaft 16 is connected to the center of the plate 30' and the arrayof beaterblades 3811-380? aresymmetrically disposed with respect totheshaft 16. The shaft 16 is, supported by a pair of thrust bearings40-, which are mounted on the supporting frame 28.

An electric motor 42 having a variable speed control and suitablysupported by a frame member 46, is coupled to the upper end of the shaft16. Other motors or drive means having variable-speed controlling meansmay be substituted for the motor 42 if desired. The duct 2'4 is alsoprovided with a cooling jacket 54 to which coolant. is applied throughthe inlet 56 and withdrawn, through the outlet 58. v a Y :The conversionchamber .12 contains a Water jacket 48 through which water or othersuitable coolantis oir: culated. The coolant is supplied to the coolingjacket through a fluid, entry inlet 50 and is Withdrawn through theoutlet 52 which is remotely disposed with respect-to the inlet. a

In operation molten slag is fed, into the slag inlet 34 and falls ontothe rotating plate 30 and beater bars .38a-38d. Particulatedcarbonaceous material, such as coal, which is pulverized to pass througha sixteen mesh screen, is simultaneously fed into the converter chamber12 through the inlet 36 and falls upon the plate 30 and heater bars,3841-3841. The pulverized coalmay be fed into the conversion chamber 12by any convenient metering means, such as, for example, by mixing thepulverized coal at the desired rate with compressed air and blowing themix: ture into the conversion chamber 12. In the embodiment of theinvention illustrated the fanning action occurring as a result of therotatingof the beater bars 38a-38d tends to somewhat retard the feedingin of particula'ted,

While pulverized bituminous coal has been specifically described as onecarbonaceous material which may be used in practicing this invention,other carbonaceous materials may be used. Pulverized saw dust, carbonparticles, or lamp black are typical carbonaceous materials which areadapted to be used with this invention.

Alternatively, good, strong, light weight aggregate has been made when agas liberating material such as baking soda has been substituted for thepulverized coal. While baking soda may he said to be a carbonaceousmaterial, other materials may be used which decompose at suitable ratesat the operating temperature of the slag and form gas inclusions withinthe slag.

The amount and type of gas liberating additive (such as pulverized coal,for example) which must be worked into the molten slag as well as therate of rotation of the agitator 14 and the cooling rate and rate offlow of the slag must be suitably determined for each type of slag whichis to be converted to light weight aggregate.

The molten slag is fed into the converter through the tube or trough 20(or by other means such as a water cooled funnel, not shown), falling asa stream onto the rotating bars 38a-38d of the beater 14. Theparticulated carbonaceous material, commonly pulverized coal, also fallsonto the rotating agitator 14, the slag and pulverized coal being mixedtogether and thrown outwardly by centrifugal force. The mixture of slag,pulverized coal and air is thrown by centrifugal force onto the slightlydownwardly diverging side walls 60 of the conversion chamber 12. Themixture of slag, pulverized coal and air is deposited as successivelayers on the walls 60 of the conversion chamber. Some of the coal burnson contact with the slag, but a substantial part of the coal remainsunburned until after the aggregate is deposited on the walls 60 of theconversion chamber. The pulverized coal dust while more or lessentrapped in the molten, plastic slag, becomes heated, therebyliberating volatile matter forming gas inclusions which cause the slag,which is still in a plastic state, to expand. Some of the coal alsoburns to produce gases.

As more of the molten slag-air-pulverized coal mixture builds up on thewalls 60, the mixture is usually forced downwardly by its own weightalong the diverging sides 60, chunks breaking 011' as the edge 41 of thechamber 12 is reached and falling onto the conveyor 13. Should the abovedescribed mixture build up heavily on the walls 60 without fallingtherefrom, the ends of the rotating beater bars 38a-38d scrape thedeposit of slag mixture and remove chunks of the plastic slag mixturetherefrom, the chunks or globs dropping onto the conveyor 13.

Because the beater bars 38a-38d often tend to fling the globs or chunksof slag mixture or aggregate outwardly, the duct 24, whose sidesconverge, is used to prevent undue scattering of the aggregate and todirect the falling chucks of aggregate onto the conveyor 13.

In one pyrolytic slag conversion apparatus made in accordance with thisinvention the diameter of the agitator 14 is approximately 19 inches andthe side walls 60 of the conversion chamber are spaced about one halfinch from the ends of the beater bars 38a 38d. The half inch spacing hasbeen found to be critical, because less spacing plugs the apparatus andmore spacing results in an aggregate having gas inclusion bubbles ofwidely varying size, which is less desirable, from a quality standpoint,for use as an aggregate in building blocks than is aggregate materialhaving relatively uniform, small gas inclusion bubbles. Four beater barsare used; the bars 38a-38d and the plate 30 being cast as an integralunit and made of a stainless steel alloy which is capable of operationat high temperatures (such as 309 Stainless steel).

Whe a s r m o mol en slag of between One-quarter inch and two inches indiameter is fed by gravity into the conversion chamber through the inletopening 34, a light weight aggregate is produced when pulverized coal(0X16 mesh size works well) is simultaneously fed into the conversionchamber 12, at a uniform rate of about 7 /2 to 30 pounds per ton ofmolten slag, and the beater bars 38a-38d are rotated to provide avelocity, at the outer end thereof, of from 3,500 feet to 4,500 feet perminute with best results occurring at a velocity of about 4,000 feet perminute.

When the above described pyrolytic conversion apparatus is used with adense, molten ash or slag, resulting from, for example, the combustionof coal at about 3,000 degrees Fahrenheit, an excellent light weightaggregate results when 10 pounds of 0x 16 mesh pulverized bituminouscoal is fed into the conversion chamber with each ton of slag and whenthe beater bars 38a-38d are rotated to provide a velocity at the outerends of the bars of about 4,000 feet per minute.

It has been found that when a dense iron aluminum silicate molten slagcomes into contact with water or water vapor it does not produce ausable aggregate. Thus, although parts of the pyrolytic conversionapparatus of this invention are water cooled, no water other than thesmall percentage composition of Water which is inherent in coal ispermitted to come into contact with the molten slag while the slag isundergoing treatment in the apparatus.

The cooling of the conversion chamber 12 and the duct 24 is controlledby adjusting the amount of water which is circulated through the coolingjackets. In the conversion chamber 12, which contains a water jackethaving about 20 gallons capacity, good results are obtained when ifabout 30 gallons of cool water per minute are circulated through thejacket. (It was found that when only 10 gallons per minute of water wascirculated through the jacket that a considerable part of the water wasconverted to steam.)

The term gas liberating material, as used herein, is intended to includenon-aqueous, solid materials which, when mixed with molten slag,liberate gas by burning, reaction with the slag, or decomposition.

Also, while half-inch spacing between the beater bars 38 and wall 60 ofthe mixing chamber 12 is preferred, a slight deviation in spacing, suchas one sixtenth inch closer to the wall or one eighth inch further fromthe wall, are operable.

What is claimed is:

1. Apparatus for converting molten iron-aluminumsilicate type slag tolight weight aggregate, comprising an inverted frusto-conical cup shapedmixing chamber having an open lower end, a closed top and downwardlydiverging side walls, said side walls diverging at at least five degreesfrom the longitudinal axis of the chamber, means for cooling said sidewalls, a rotatable agitator having an axis of rotation and a pluralityof blade-like elements disposed in a symmetrical array about said axisof rotation, said agitator being disposed within and axially alignedwith respect to said chamber, each of said bladelike elements havingends which are spaced from said side walls of the mixing chamber byapproximately one half inch, means for directing molten slag onto saidblade-like element, and means for metering particulated gas liberatingmaterial onto said agitator.

2. Apparatus in accordance with claim 1, wherein said agitator comprisesa hub having a plurality of bladelike elements extending therefrom.

3. Apparatus in accordance with claim 1, wherein a water jacketed ductwork skirt encircles said chamber and extends downwardly from thechamber, the angle made by the skirt with respect to the longitudinalaxis of the chamber being between zero and ten degrees.

4. Apparatus in accordance with claim 1, wherein means are provided forrotating said agitator.

5. Apparatus in accordance with claim 1, wherein said means for coolingsaid side walls is a fluid cooling jacket adapted to be connected to asource of coolant fluid.

6. Apparatus in accordance with claim 4, wherein means are provided forcontrolling the rate of rotation of said agitator.

7. Apparatus in accordance with claim 1, wherein said means fordirecting molten slag and means for directing a metered amount ofparticulated gas liberating material each includes an aperture in thetop of said mixing chamber, each of said apertures being disposed abovesaid agitator.

References Cited in the file of this patent UNITED STATES PATENTS

